The invention relates to improvements in synthetic turf for sports fields and the like, and particularly to synthetic turf which remains cooler under the sunlight.
It is believed that the present invention will materially enhance the quality of the environment of mankind by contributing to the maintenance of the basic life-sustaining natural elements. In particular, the present invention employs environmentally benign colorants, such as chlorophyll, in place of pigments, which may incorporate heavy metals. Artificial turf containing the benign colorants may be disposed of without contaminating the soil, and temporary coatings containing the benign colorants can be rinsed off without contaminating water.
The first synthetic turf was called Astroturf made with nylon fiber and was used in the mid 1960s to the early 1990s for most playing field applications, i.e., football, baseball, soccer, etc. The nylon fibers were very abrasive, which led to the development of polyolefin fibers, primarily polyethylene and polypropylene. Polyolefin fibers exhibit significantly lower abrasive characteristics, thus minimizing skin burns. Many improvements in the looks and durability have been made to artificial turf, but a significant drawback remains, namely the propensity of artificial turf to absorb infrared solar radiation and retain heat.
Studies have shown that artificial turf can reach temperatures that are 80° F. or greater than natural turf, under similar conditions. The surface of artificial turf has been measured to reach temperatures as high as 157° F. This elevated temperature of artificial turf can be unpleasant for sports participants, and even, at times, unsafe.
Disposing of artificial turf after its life has become a challenge due to its chemical make-up, and is considered hazardous in some geographic locations. The use of inorganic colorants, especially colorants containing heavy metals, exacerbates disposal of artificial turf.
The use of polyolefins in general, and polyethylene and polypropylene in particular, to manufacture synthetic turf is disclosed in Published Application US2007/0154661 A1 and U.S. Pat. No. 3,731,923. The use of pigments, in general, to provide a desired shade of color to the turf, is also known.
Chlorophyll and its derivatives have been used in various applications. U.S. Pat. No. 5,645,933 discloses copper chlorophyll and sodium iron chlorophyll as examples of pigment for use in polypropylene fabric used as tarps, house wraps, etc. U.S. Pat. No. 6,134,718 discloses impregnating garment fabric with chlorophyll to absorb odors. U.S. published application 2003/0138653 discloses using transparent or semi-transparent film for food packaging containing chlorophyll or chlorophyllin.
Conventional green pigments do not resemble chlorophyll in the infrared region, that is, they absorb infrared light, whereas chlorophyll reflects it. In camouflaging military equipment and installations, however, it has been found that chromium oxide pigments reflect infrared radiation similar to chlorophyll, so that the camouflage appears as natural foliage. The chromium oxide pigments may be incorporated in polyurethane, silicone elastomer and/or polyvinylidene coatings and fibers used in camouflage, as disclosed in U.S. Pat. Nos. 6,454,848; 6,589,297; 7,148,161; and 7,244,684.
A strong need remains for an artificial turf that stays relatively cool when exposed to solar radiation. Furthermore, any modifications to improve the heating characteristics of artificial turf should have a minimal adverse environmental impact, both from the viewpoint of day-to-day operations and with regard to disposal of the artificial turf, after its useful life.